React Essentials · Data Fetching · Lesson 17 of 26

Fetching Data with useEffect

Concept

Fetching Data with useEffect

Combine fetch() with useEffect to load data when a component mounts.

By the end of this lesson

Explain the core idea behind Fetching Data with useEffect.
Predict output before running a change.
Test one realistic and one unusual input.
Use the result to make the next decision.

How to study this page

1. Read one concept.
2. Change the example.
3. Run, compare, and explain.
4. Complete the challenge below.

ExampleRunnable

useEffect(() => {
  fetch("/api/courses").then((res) => res.json()).then(setCourses);
}, []);

Try it Yourself »

Self-check before continuing

Without looking at the example, describe what changes when you modify one input in Fetching Data with useEffect. Then reopen the editor and prove your explanation with a small test.

You are ready to continue when you can predict, test, and explain the result.

Your turn

Describe what the empty dependency array means for when this effect runs.

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Console

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